Method for freeze-drying and freeze-dried product

ABSTRACT

A process for producing a freeze-dried product in a bonded or stratified state by a simple apparatus and by simple operations, without suffering from denaturation by oxygen, enzymes, heat and so on, while maintaining the original quality, properties and so on, by bonding or stratifying materials to be treated before being subjected to freeze-drying; an apparatus therefor; and a freeze-dried product obtained therefrom are provided. The freeze-dried product is obtained by stratifying materials  7   a   , 7   b  and  7   c  of the same or a different kind to be treated into a multilayer under interposition of dry ice  6   b   , 6   c  partly in between the layers; pressing the multilayer from both sides by pressurizing elements  13  and  16  under intermediation by dry ice  6   a  and  6   d  to effect bonding of the materials to be treated with each other, while, at the same time, freezing the multilayer; and subjecting the frozen product to vacuum drying.

FIELD OF THE INVENTION

The present invention relates to a process for freezing or freeze-dryinga material which is susceptible to denaturing, such as a food or drink,a living organism, organic material, drug, biological sample, feed orindustrial raw material, a frozen or freeze-dried product obtained bysuch a process and to an apparatus for effecting the freezing orfreeze-drying.

BACKGROUND OF THE INVENTION

For storing, transporting and bringing into practical use materialssusceptible to denaturing, comprising organic substances, such as foodsand drinks, living organisms, such as animals, plants and microbes,organic materials, drugs, biological samples, feeds and industrial rawmaterials, they are often subjected to freeze-drying. For example, foodsand drinks, especially food products are freeze-dried for storing andtransporting and are brought into dietary services in the freeze-driedstate as such or after being hydrated with the addition of water orfurther processed. In the case of biological samples, they are preparedby a series of operations for processing a living organism by, forexample, freezing, drying, crushing and homogenization.

The freezing procedure for freeze-drying may generally be realized usinga refrigerator. Here, it takes a prolonged period of time until thefreezing temperature is reached, during which the material to beprocessed may suffer from denaturation due to the action of oxygen orenzymes. Even if the frozen material is subjected to vacuum drying, afreeze-dried product without being subjected to denaturation may bedifficult to obtain. When a food is frozen in a refrigerator and, then,freeze-dried, so-called shrinkage phenomenon may occur, in which, due toshrinkage and drying of, for example, cellulosic tissues of brake,tissues of, for example, muscles of cuttlefish and cell walls ofchlorella, they are converted into dried brake, dried cuttlefish andchlorella beads or in which, due to the contraction of an internal massof, for example, cheese, into an isolate solid lump inside the mass toform an internal cavity, whereby a decrease in the taste or feel inmouth undesirably results with a concurrent lowering of the digestion ofsuch food.

Freeze-drying may often by practiced after the material to be processedhas preliminarily been treated by, for example, crushing and forminginto thin films, in order to increase the drying efficiency. Such acrushing operation may cause a temperature elevation of the material dueto a heat evolution upon crushing. The material to be processed maysuffer from denaturing due to such a temperature elevation and due toenzymes present in the system, so that the freeze-drying may not berealized under crushing and forming into thin films while preserving theoriginal quality and condition of the material.

For eliminating such difficulties, it has been practiced to freeze thematerial using liquid nitrogen or, in addition, to exclude oxygen.However, such countermeasures require, due to the very low temperatureof liquid nitrogen (minus 196° C.), large scale arrangements and, due tothe exclusion of oxygen, a safety measure, so that a freeze-driedproduct may not be obtained in an easy and convenient way.

An object of the present invention is to provide a method for producinga freeze-dried product of a material to be processed, by subjecting itto freezing and vacuum drying by a simple apparatus and simpleoperations, in a state in which the intrinsic quality and properties,etc., of the original material are preserved without suffering fromdenaturing of the material due to the actions of oxygen, enzymes, heatand so on; to provide an apparatus therefore; and to provide afreeze-dried product obtained therefrom.

Another object of the present invention is to provide a process forproducing a freeze-dried product of a material in a bonded or in astratified state, by subjecting the material to freeze-drying underbonding or stratifying of the material, while preserving the intrinsicquality and properties, etc., of the original material using a simpleapparatus by simple procedures without suffering from denaturing of thematerial due to the actions of oxygen, enzymes, heat and so on; anapparatus therefor; and a freeze-dried product obtained therefrom.

DISCLOSURE OF THE INVENTION

The present invention consists of the following process forfreeze-drying, apparatus therefor and freeze-dried product:

(1) A process for freeze-drying, comprising cooling one or morematerials to be treated, in a state separated from or in contact witheach other, by dry ice to freeze the material(s) and subjecting thefrozen product to vacuum drying.

(2) A process for freeze-drying, comprising stratifying materials of thesame or different kind to be treated into multilayers, freezing themultilayers in a state in which dry ice is interposed between the layersand subjecting the frozen multilayers to vacuum drying.

(3) The process as defined in the above (2), wherein dry ice isinterposed between the layers partly so as to leave the portions devoidof dry ice in a state adhered to each other, in order to form a vacantspace at the portion where dry ice is interposed.

(4) The process as defined in any one of the above (1) to (3), whereinthe freezing is effected under a condition pressurized by the material'sown weight or by an external pressure.

(5) The process as defined in any one of the above (1) to (4), whereinthe freezing is effected while breaking the material to be treated bypressurizing it so as to cause formation of cracks.

(6) A freeze-dried product obtained by the process as defined in any oneof the above (1) to (5).

(7) Foods and drinks comprising the freeze-dried product as defined inthe above (6).

(8) A composite product in which the freeze-dried product as defined inthe above (6) is compounded with other material(s).

(9) A hydrated product obtained by hydrating the freeze-dried product asdefined in the above (6).

(10) A composite product in which the hydrated product as defined in theabove (9) is compounded with other material(s).

(11) An apparatus for effecting freeze-drying, comprising

a freezing apparatus in which one or more materials to be treated arecooled in a state in which they are separated from or in contact witheach other by dry ice to freeze the material(s) and

a vacuum drying apparatus in which the frozen product obtained in thefreezing apparatus is subjected to vacuum drying.

(12) The apparatus as defined in the above (11), wherein the freezingapparatus operates to freeze multilayers of the material to be treatedunder a condition in which dry ice is interposed between the layerspartly.

(13) The apparatus as defined in the above (11) or (12), wherein thefreezing apparatus comprises a pressurizing means.

(14) The apparatus as defined in the above (13), wherein the freezingapparatus comprises pressurizing elements which operate to impress apressure onto a single layer or multilayers of the material placedtherebetween together with dry ice.

(15) The apparatus as defined in the above (14), wherein the freezingapparatus comprises a traveling means operable to cause the pressurizingelements to travel within a pressurization unit.

(16) A method of analysis, in which the freeze-dried product defined inthe above (6) is used as the analytical sample.

(17) An apparatus for analysis, in which the freeze-dried productdefined in the above (6) is used as the analytical sample.

The materials to be treated by freeze-drying according to the presentinvention are those susceptible to denaturation, including foods anddrinks, organisms, organic materials, drugs, biological samples, feedsand industrial raw materials, in particular those comprising organicmaterials having reducing functional groups susceptible to denaturing bythe actions of oxygen, enzymes, heat and so on. They may be present inany voluntary form, such as a lump, liquid, jelly, paste or slurry,including crushed or pulverized form. Typical materials to be treatedmay be in a hydrated state, though dried materials may be included solong as they permit processing, e.g. homogenization, by mixing withwater or with hydrated materials.

Further, materials which are not susceptible to denaturation, includingfilter paper, textiles, non-woven fabrics, nets, films, sheets andplates, may also be subjected to freeze-drying by treating them togetherwith the above-mentioned material susceptible to denaturation in a stateintegrated bodily therewith.

The foods and drinks, organisms, organic materials, drugs, biologicalsamples, feeds and industrial raw materials and so on are not enumeratedas parallel concepts but fall under a mere exemplification of materialscapable of being treated. The foods and drinks may be in a solid orliquid state, wherein those having consistencies or water contentspermitting stratification may be used for being stratified as thematerial to be treated. The foods and drinks may be composed essentiallyof organic materials, though inorganic materials may also be included.As the organism, whole bodies or a part (a tissue) of an individual ofan animal or plant, cells and microorganisms, such as chlorella,Spirillina and so on, may be dealt with. As the organic materials, notonly such organisms as above, but also those organic substances derivedfrom such organisms may be dealt with. While the feeds, drugs andindustrial raw materials may generally comprise living organisms andorganic materials, inorganic materials may also be dealt with inaccordance with the present invention so long as they are susceptible todenaturation. The biological samples may, in general, be analyticalsamples consisting of organisms, though other samples may also be dealtwith.

Dry ice may be a compacted product of solid carbon dioxide whichsublimates at −78.5° C. under atmospheric pressure. Any commercialproduct sold as a coolant or the like may be used as dry ice. Such a dryice product can be crushed easily by applying a compressive forcethereto in a mixer-crusher and, thus, can be used in a voluntary formand size, wherein, for example, a product having particle sizes of about1-10 mm may be preferable. The amount of dry ice to be used may varydepending on the kind, moisture content, consistency and so on of thematerial to be treated, while it may in general range from 0.01 to 5parts, preferably from 0.05 to 1 part by weight per one part by weightof the material to be treated. In the case where dry ice is placedbetween layers, it is favorable to use dry ice having a particle size of1-5 mm in an amount of 0.01-0.5 part by weight, preferably 0.05-0.1 partby weight, per one part by weight of the material to be treated.

According to the present invention, one single material or a pluralityof materials to be treated are cooled by dry ice in a state separatedfrom or in contact with each other to cause them to freeze and, bysubjecting the frozen product to vacuum freezing, a freeze-dried productis produced. When the material to be treated is frozen in the originalstate as such, the material can be frozen in a sole piece or in piecesisolated from each other. For example, fruits, vegetables and the likemay be frozen as a whole body or in cut pieces. A material to be treatedwhich is in a form of liquid, slurry, paste or so on can be frozen intoa single layer or frozen product by filling or piling it in or on avessel.

In the case of producing a freeze-dried product in which a plurality ofmaterials to be treated are bonded together, the plurality of materialsto be treated are subjected to freezing under a state in which thematerials are in contact with each other to thereby cause the materialsto adhere to each other at the contacted areas, whereby a frozen productin which a plurality of materials are bonded together is obtained, fromwhich a freeze-dried product containing a plurality of materials to betreated in a state adhered to each other is obtained by vacuum drying.Here, the materials to be bonded together may be of either the same or adifferent kind. The material may have a skin, as in the case of a fruit,and may favorably have a water content of 10% by weight or more,preferably 10-90% by weight.

It is also possible to bond a hydrous or a fibrous material with an oilymaterial. For example, a hydrous material, such as a vegetable or afruit, may be bonded to a fatty substance to freeze-dry the bondedproduct. Here, it is possible to effect the freeze-drying for a producthaving the fatty substance under impregnation, such as a fried food,though it is permissible to integrate the fatty substance with a hydrousor fibrous material on the surface thereof. In the case of the latter,it is possible to effect the integration by coating on the surface ofthe hydrous or fibrous material with the fatty substance and freezingthe coated product or, alternatively, by forming a layer of the fattysubstance on the surface of a pressing member, scattering dry icethereonto over partial areas thereof and placing thereon the hydrous orfibrous material, whereupon the resulting lamination is frozen to bebodily integrated while pressing it. By bonding a layer of a fattysubstance to the surface in this manner, a freeze-dried product whichcan easily be swallowed can be obtained.

When the material to be treated subject to denaturation is to beintegrated with a material to be treated not subject to denaturationused as a support, such as filter paper, non-woven fabric, net, film,sheet or plate, the support material may be bonded with the hydrousmaterial to be treated under intermediation by dry ice or by coolingwith dry ice to effect freeze-drying, in order to obtain a freeze-driedproduct in which they are integrated. When the material to be treatedsubject to denaturation is put between two pieces of a support materialto integrate them, the integrated product can serve as, for example, ananalytical sample, since 100% recovery of the freeze-dried product ofthe material to be treated can be attained. When, in this case, theintegration is effected while pressing the product together with a hardsubstance, such as glass fiber, aramid fiber or ceramic powder, thematerial to be treated may be recovered as a freeze-dried product in astate in which it is caused to collapse by the hard substance at anultralow temperature or in which fibers are stuck into the material, sothat it can be used, for example, for extracting a sample for analysisand for extracting a food constituent, such as a flavor or so on.

While it is favorable, for bonding a plurality of materials to betreated to each other, that each has a face for being bonded together,bonding may be attained even for materials having a convex face to bebonded, so long as these faces can be deformed by being pressed togetherinto faces adapted to be bonded together and, in particular, the bondingadhesion may be increased when water exudes from inside during thepressing together and is frozen. The pressing of the materials onto eachother may be effected by the weight of the material or in a mechanicalway.

It is possible, for producing a freeze-dried product of multilayersbonded with each other, to effect bonding of the layers with each other,by stratifying stratiform materials of an identical or a different kindover one another and freezing the stratified product, wherein dry icemay be interposed between the layers in partial areas thereof, wherebythe layers can be bonded together at the portions devoid of dry ice andvacant spaces can be formed at the portions interposed by dry ice.

The materials to be treated are cooled and frozen within a short periodof time by bringing the materials and dry ice placed in a freezingapparatus into contact with each other. As the freezing apparatus, anyone may be used so long as it is constructed to permit the accommodationof the materials to be treated and dry ice therein in a mixed state andto bring them into contact, wherein it is favorable that the apparatusis so constructed as to subject the materials and dry ice to be pressedby their own weight or by an adequate mechanical or other means. In thecase of bonding a plurality of materials to be treated, it is favorableto construct the freezing apparatus in such a manner that the bondingcan be realized under pressing in a direction vertical to the bondedplane.

When the material to be treated is brought into contact with dry ice,the gas phase is replaced by evolved carbon dioxide gas to excludeambient oxygen, while realizing at the same time a prompt freezing ofthe material to build up a frozen product. Dry ice may preferably bemixed in a form of crushed fine particles with the material to betreated, whereby the ambient air is replaced by the carbon dioxide gasevolved by heat absorption upon contact with the material to build up aninert atmosphere while causing the material to be frozeninstantaneously.

If the material to be treated is present in a form of lumps of arelatively large particle size, freezing may require a somewhat longertime. However, when the material to be treated is partly broken beforeor after the freezing or simultaneously with the freezing, the freezingprogresses also from the broken sites, whereby the freezing will becompleted within a short period of time. In the case where the materialto be treated is in a form of a liquid, jelly, slurry or the like, thefreezing starts from a portion exposed to the outside or a portioncontacting with dry ice. By pressurizing, also in this case, frozenportions become broken to cause thereby a region of a liquid state to beexposed, which is then frozen upon contact with dry ice. Such processesproceed within a relatively short period of time, whereby freezingoccurs as a whole substantially instantaneously.

In this manner, by the contact of the material to be treated with dryice, the ambient oxygen is replaced by carbon dioxide gas to establishan inert atmosphere with simultaneous freezing of the material suddenly,whereby enzymes will be deactivated and the material does not sufferfrom denaturation. Thereby a frozen product is obtained, in which eachcomponent, taste, color and other properties of the original materialare retained as such. Even in the case where the material to be treatedis subjected to mixing and breaking in the course of freezing, the heatdeveloped thereby can be cooled by dry ice and will not cause anydenaturation of the material but, rather, can favorably function togenerate carbon dioxide gas to sweep off oxygen.

For bonding a plurality of materials to be treated, a plurality ofmaterials held in contact with each other may be brought into contactwith dry ice to cool them, whereby they adhere to each other and arefrozen in this state. Such a phenomenon resembles the case where a barehand adheres to a chilly wall surface in a cold season. Thus, thematerials to be treated adhere to each other and are frozen in thisstate, whereby a bonded frozen product is obtained. The material to betreated will be deformed by pressing the bonded boundary face to spreadthe adhering interface to intensify the adhesion. If a liquid exudesfrom inside by pressing, the adhesive strength is further increased dueto freezing of the liquid.

When a plurality of the materials to be treated are stratified intomultilayers and the multilayers are frozen in a state in which dry iceis interposed between the layers partly, freezing proceeds by coolingfrom outside while, at the same time, freezing occurs also from insidedue to cooling on the carbon dioxide gas evolved by the gasification ofdry ice interposed between the layers leaving the portions where no dryice is present in a state adhered to each other, whereby the freezingtime may considerably be reduced together with attainment of preventionof debasement of quality and an increased adhesive strength. On progressof freezing, the portions of the layers where the dry ice interposedbetween the layers has disappeared will be brought into adhesion to eachother, whereas the portions where dry ice remains will be frozen into afrozen product containing dry ice enclosed in such portions.

For the freezing apparatus, there may be employed those having astructure in which the material to be treated is accommodated simplytogether with dry ice to achieve cooling, those having a structure inwhich a means for blending and/or breaking is installed and those havinga structure in which a pressurizing means is arranged. For thepressurizing means, there may be exemplified those in which thepressurization is effected in order to destroy the material partly andthose in which the pressurization is effected in order to cause bondingof a plurality of materials to be treated. For the pressurization, theremay be recited, for example, use of a piston-like pressing means and atechnique in which the material to be treated is caused to travel forthe extent over the pressing means under a condition of being pinched inbetween pressing boards.

One favorable method for stratifying and freezing the material consistsof placing a piece of the material to be treated on a lower mold half(concave mold) made of Teflon (tetrafluoroethylene resin) cooled by dryice or liquid nitrogen or in a refrigerator, roughly sprayed dry icepartly over the upper face of the material to be treated, placingthereon another piece of the material to be bonded therewith at normaltemperature before the entire upper face of the first said piece of thematerial has been frozen, performing, if necessary, stratification onthe so-stratified product by similar procedures to obtain multilayersand spraying dry ice particles on the uppermost layer to effect freezingof the multilayers while pressing the multilayers from above by an uppermold half (convex mold). Here, it is favorable to forward the materialto be treated by rotating rollers arranged in the pressurizing sectionby a motor, whereby the process steps of freezing, bonding and moldingcan be carried out automatically. The pressure in the pressurizingsection may range from 0.001 to 200 kN and may be 0.001-0.1 kN for asoft material, such as a strawberry, and 30-200 kN for a material havinghard cell walls, such as chlorella.

The frozen product obtained as above may be subjected, directly or afterhaving been stored and transported in the frozen state, to vacuum dryingunder a frozen state using a vacuum drying apparatus to produce afreeze-dried product. By placing the frozen product in a vacuum dryingapparatus to maintain it under a vacuum condition, the freeze-driedproduct is obtained by drying under sublimation of humidity and dry icecontained in the frozen product. The degree of vacuum during the vacuumdrying may be 1-50 Pa, preferably 1-5 Pa. Here also, there is no fear ofdenaturation, since the drying is realized in an inert atmospherewithout passing through a liquid phase. In the case of a frozen productin which dry ice is enclosed in the inside as in the case where thefreezing is effected in a multilayered state, a high vacuum dryingefficiency may be attained and the drying can be realized within a shortperiod of time, since the sublimation of ice is effected in a state ofbeing rendered porous by the preceding sublimation of dry ice.

The so-obtained freeze-dried product is held under a condition in whichthe components, color, gustative taste, fragrance, flavor, mouth feel,physico-chemical properties and so on of the original material beforethe treatment are maintained and may be brought into a finished productafter having been subjected, if necessary, to processing operations,such as cutting, crushing and so on. The freeze-dried product isobtained under a condition of not contacting with oxygen and can bestored, transported and serve for practical use in the inert state assuch, while it may scarcely suffer from denaturation, even if it isstored and transported under a condition of being sealed with theaddition of a deoxidant so long as it is not caused to absorb humidity.A freeze-dried product obtained by freeze-drying a plurality ofmaterials to be treated under a condition of contacting with each otheror being stratified into multilayers may preserve its bonded orstratified state without separation of the bonded part.

In the practice of the present invention, when cracks are formed in, forexample, fibrous tissues, such as cellulose and muscle, and the cellwalls of organisms, such as animals, plants and microorganisms, of thematerial to be treated, the surface area of contact will be increased tothereby increase the strength of adhesion between the materials to betreated, with simultaneous attainment of prevention of separation of thebonded part due to shrinkage, hardening or the like, whereby it is ableto alter the tissue structure in such a manner that the internalcontents of the tissue or the contents of the cells of the material tobe treated can easily exude out to increase the rate of digestiontogether with softer mouth feel.

For the materials to be utilized as the freeze-dried product, anyvoluntary substance including bodies of organisms and organic materialsmay be enumerated. Specific examples include foods, such as vegetables,fruits, meats and dairy products; medicines, such as crude drugsobtainable from organisms; bodies of organisms; samples of organisms foranalytical purpose in which tissues or so on are homogenized; bacterialcells of, such as yeasts and bacteria; and industrial raw materials,such as doughs, starches and proteins. Bacterial cells will lose theirproliferative activity by the formation of cracks in the cell walls andmay occasionally become inviable by the destruction of the cell walls,while, in such cases, use as vaccines may be permitted, since thedestruction of cell walls can be realized without any damage ofcorresponding proteins to serve as an antigen. When miscellaneousbacteria are inviable by increasing the impressed pressure, safety offoods and so on are increased.

The freeze-dried product can be used in the dried state as such inaccordance with the purpose, while it may be used in the restored stateby hydrating it or, further, after being subjected to processings, suchas heating etc. The material to be treated will be restored by hydrationto the original state before the freeze-drying and the taste, gustativetaste, fragrance and so on will also be regained. A bonded productobtained by bonding a plurality of materials to be treated or amultilayered product resulting from the stratification of them willmaintain the bonded or stratified state without causing any peeling-offeven after having been regained by water and the bonded or stratifiedstate is kept even after having been subjected to processing operations,such as heating etc.

While the freeze-dried product can be used in the state as such or afterhaving been hydrated or processed, as given above, it may be used undercompounding with other materials. For example, in the case of using thefreeze-dried product for a food or a drink, a superior composite food ordrink can be obtained by compounding or processing and cooking ittogether with a jelly, chocolate, juice, milk, cream, bread dough, cakedough, pasta, rice, vegetable or so on. In these cases also, thefreeze-dried product maintains its fresh state before the freeze dryingand elution of soluble components, such as sugars, acids, enzymes and soon is scarce.

When fruits and vegetables, such as raisins, pumpkins and carrots, areadded to bread or pie, the border of them may, in general, become stickydue to exudation of moisture and sugars from such an additive. However,when the freeze-dried product according to the present invention isemployed, such a sticky feel is eliminated and superior appearance andsuperior mouth feel are attained. When apple, kiwi fruit or the like areadmixed to milk, cream, white chocolate or the like, coagulation ofproteins, such as casein, may occur due to the presence of an acid.When, however, the freeze-dried product according to the presentinvention is used, no acid is eluted and coagulation does not occur,whereby a smooth mouth feel can be attained. While there occurs nocoagulation by mixing a fruit or other having a content of aprotein-decomposing enzyme, such as kiwi fruit, with jelly, no suchproblem occurs when the freeze-dried product according to the presentinvention is mixed, and coagulation of jelly occurs. Thus, even using acomponent which is difficult to be compounded due to their influence oneach other, a composite product of, for example, a food or a drink,which is not influenced by each component, can be obtained when thefreeze-dried product according to the present invention is compoundedwith the other material.

By the process and apparatus for freeze-drying according to the presentinvention, a material to be treated can be freeze-dried whilemaintaining the quality, properties and so on before the treatment,without suffering from denaturation by oxygen, heat and so on, togetherwith reduction of the time required for the drying, and, in addition, bysubjecting a plurality of materials to be treated with each other in acontacted or stratified state, a freeze-dried product in which thematerials to be treated are bonded or stratified can be obtained, sinceone single material or a plurality of materials to be treated arevacuum-dried after having been cooled and frozen by dry ice in a stateof being isolated from or contacted with each other.

The freeze-dried product according to the present invention is inert andmaintains the original quality, properties and so on before thetreatment and a freeze-dried product in which a plurality of materialsto be treated are bonded together or stratified one over another can beobtained. It can be stored, transported and used as such and can beutilized for a food, medicine, feed or so on having high functionalperformances. Here, a food or so on which is safe for a long period oftime can be obtained by causing bacteria to be inviable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the construction of an embodiment of a freeze-dryingapparatus.

FIG. 2 shows an embodiment of a freezing apparatus in a sectional view.

FIG. 3 shows another embodiment of the freezing apparatus in a sectionalview.

THE BEST MODE FOR EMBODYING THE INVENTION

Below, some embodiments of the present invention are described withreference to the drawings appended.

FIG. 1 shows the structure of an embodiment of a freeze-drying apparatusin an exploded view. FIGS. 2 and 3 show another embodiment of thefreezing apparatus in sectional views.

In FIG. 1, 1 denotes a freezing apparatus and 2 is a vacuum dryingapparatus. They are so constructed that the material to be treated anddry ice are supplied to the freezing apparatus 1 via a supply line 3 toeffect freezing and the resulting frozen product is transferred to thevacuum drying apparatus 2 via a transfer line 4 to subject it to vacuumdrying, whereupon the freeze-dried product is taken out via a take-outline 5.

In the freezing apparatus shown in FIG. 2, a casing 11 of a cylindricalform has a support 12, on which a ram top 13 serving as a pressurizingelement is supported slidably so as to permit movement in the verticaldirection by a hydraulic cylinder 15 via a ram rod 14 connectedunderneath. Opposing the ram top 13, another ram top 16 serving as apressurizing element is arranged slidably and is permitted to move inthe vertical direction by a hydraulic cylinder 18 via a ram rod 17connected above. In the vicinity of the upper end of the casing 11, thesupply line 3 and the transfer line 4, both in the form of a beltconveyer, are disposed. 19 is a pusher.

For performing the freezing by the freezing apparatus given abode, dryice 6 a of a particle size of, for example, 1-5 mm is supplied on theram top 13 over the entire surface thereof, while the ram top 16 is heldat an elevated position where it is receded somewhat from the upper endof the casing 11, so as to pile up to a depth of, for example, 3-7 mm.Thereon are placed then, as a material to be treated 7 a in a layeredform, for example, sliced pieces of kiwi fruit having a thickness of5-10 mm, on which dry ice particles 6 b are piled sparsely (partly),whereupon, for example, strawberry slices, as a material to be treated 7b, are placed thereon, on which, further, dry ice particles 6 c arepiled sparsely, whereupon, furthermore, a material to be treated 7 c isplaced thereon, which is then covered by dry ice particles 6 d up to adepth of 5-15 mm.

Then, in this state, the ram top 16 is caused to descend using thehydraulic cylinder 18 to effect pressing to thereby cause the materialsto be treated 7 a, 7 b and 7 c to adhere to each other at the portionsdevoid of dry ice 6 b and 6 c and to cause at the same time the freezingof the entire composite. Here, the dry ice piles 6 a and 6 d presentabove and underneath cause cooling from outside, while cooling iseffected also from inside by the interlayer dry ice piles 6 b and 6 cwith simultaneous replacement of the gas phase, whereby the materials tobe treated 7 a, 7 b and 7 c are frozen in a state adhered to each otherto obtain a frozen product.

The frozen product is raised by causing the ram top 16 to ascend whileraising the ram top 13, whereupon it is taken out on the transfer line 4by extending the pusher 19 and is transferred to the vacuum dryingapparatus 2, where it is subjected to vacuum drying to produce afreeze-dried product.

The freezing apparatus shown in FIG. 3 is so constructed that aplurality of pressurizing rollers 23 a are arranged upwardly andsupported by means of a bearing element 24 a on a bed plate 22 disposedon a bottom wall 21, in which each roller 23 a rotates in the samerotational sense (for example, counterclockwise, seen on the Figure) bymeans of a motor M. A the top, a deck 26 provided thereon with ahydraulic cylinder 27 is supported on support frames 25. Beneath a ramtop 29 arranged at the end of a ram rod 28 extending down from thehydraulic cylinder 27, a plurality of pressurizing rollers 23 b arearranged downward, supported by a bearing element 24 b. 31 and 32respectively represent a lower mold half (concave mold half) and anupper mold half (convex mold half) of a forming mold made of Teflon(tetrafluoroethylene resin), respectively, as the pressurizing elements.

For performing the freezing on the apparatus given above, the lower moldhalf 31 is charged with dry ice 6 a-6 d and the material to be treated 7a-7 c in a similar construction as in FIG. 2, whereupon the end of theupper mold half 32 is inserted in the lower mold half and, in thisstate, the lower mold half 31 and the upper mold half 32 of the formingmold are moved in the direction indicated by the arrow ‘a’ between thepressurizing rollers 23 a and 23 b, before bonding, molding and freezingare effected by pressing the ram top 29 downwards by actuating thehydraulic cylinder 27 in the manner similar to the case of FIG. 2. Sincethe pressurizing rollers 23 a rotate in the same direction by the motorM, the mold is moved out in the direction indicated by the arrow ‘b’.

While it is permissible to perform the above process steps of moving-inof the mold, pressing thereof by the hydraulic cylinder 27 andmoving-out thereof by the motor M independently, they may be carried outtotally in a continuous way. Thus, a continuous processing may berealized by moving the mold 31, 32 into the interspace between thepressed rollers 23 a, 23 b continuously to effect the pressurization andmoving it out then directly therefrom, whereby an increase in theproduction efficiency can be attained. In both cases, automaticoperation of the apparatus can be realized.

By opening the so-moved-out mold, taking out the frozen product andtransferring the frozen product to the vacuum drying apparatus 2 tocarry out vacuum drying, a freeze-dried product is obtained. When afluororesin, such as tetrafluoroethylene resin or the like, is employedfor the forming mold, a better performance in separation from the moldis attained. Dry ice piles 6 a and 6 d may facilitate mold separation,since dry ice functions also as a separating agent. However, it ispermissible to install a mechanical means for effecting removal of themolding from the mold.

The vacuum drying apparatus 2 is an apparatus for effectingvacuum-drying under a reduced pressure established by a vacuum pump, forwhich a commercial unit comprising a heating unit for increasing thesublimation velocity by heating the material to be treated at atemperature of 20-30° C. and a refrigerator for cooling the cooling coilserving for trapping the sublimated moisture at minus 50° C. may beemployed.

Below, the present invention will be described by way of Examples.

EXAMPLE 1

Using a freezing apparatus as shown in FIG. 3, a freeze-dried productwas produced. As materials to be treated 7 a and 7 c, slices of kiwifruit having a thickness of 5-10 mm and, as the material to be treated 7b, slices of strawberry having a thickness of 5-10 mm were employed. Dryice having a particle size of 3 mm was used and was piled in a thicknessof 5 mm for the lower layer 6 a and a thickness of 10 mm for the upperlayer 6 d and was scattered in the interlayer portions 6 b and 6 csparsely in an amount of 1-2 particles per cm². A frozen product wasobtained under impression of a pressure of 10 N for 60 seconds. Thefrozen product was transferred to a commercial vacuum drying apparatusand subjected to vacuum drying under a degree of vacuum of 2 Pa for 48hours at a drying tray temperature of 20° C. to produce a freeze driedproduct.

The resulting freeze-dried product consisted of multilayers in which thematerials to be treated 7 a, 7 band 7 c were bonded to each other and noseparation occurred after they were restored with water, wherein thecolor, taste and fragrance were maintained under the original state.

In general, when a raw kiwi fruit or raw strawberry is admixed with milkor a dairy product, coagulation of casein, a protein, occurs by theorganic acids present in the fruit. However, there occurred nocoagulation by admixing of the freeze-dried products, whereby dairyproducts with a smooth mouth feel, such as processed dairy products,yogurt and white chocolate, could be produced.

When a bread and a pie containing a freeze-dried product of pumpkin andcarrot were prepared, there occurred no portion of a sticky structure asappears in the case of blending with raw pumpkin or raw carrot and abread or pie exhibiting crispy mouth feel was able to be produced.

EXAMPLE 2

Using an apparatus as shown in FIG. 3, pieces of raw kiwi fruit (majordiameter of 30-60 mm, minor diameter of 30-45 mm) cut in a thickness of10 mm and pieces of cylindrically cut raw papaya (diameter about 20 mm,thickness 10 mm) inserted in each central portion of each piece of kiwifruit, as the materials to be treated, were placed on a layer of dry icespread in a pressing vessel and, then, granular dry ice was scatteredsparsely over the surface, whereupon the composite was subjected to aweak pressing at 10 N for one minute to cause a partial breaking down ofthe materials to be treated, in order to subject it to a freeze-dryingunder a condition in which slight cracks were formed. As a result,light-colored dry products were able to be prepared, in which thefragrances of the fruits were better preserved. When the observedcalorimetric values of a luminosity of about 50, a b-value of about 24,yellow, for the freeze-dried product of kiwi fruit are compared withthose of the raw kiwi fruit, the luminosity was increased by about 60%and the b-value was reduced by about 30%. When the observed values ofthe luminosity (about 75) and the b-value (about 50, yellow) for thefreeze-dried product of papaya are compared with those of the rawpapaya, the luminosity was increased by about 10% and the b-value wasreduced by about 60%.

When cakes were prepared by enclosing these freeze-dried products in alayer of transparent jelly, the b-value for kiwi fruit was restorednearly to that of raw kiwi fruit. The luminosity showed a valueintermediate between that of the freeze-dried product and that of theraw fruit. While the luminosity of papaya was nearly the same as that ofthe raw fruit, the b-value showed an intermediate value between thefreeze-dried fruit and the raw fruit.

While raw kiwi fruit and raw papaya do not show coagulation of jelly dueto their content of a protease for decomposing proteins, such as jelly,it was possible to prepare a completely coagulated jelly by using thefreeze-dried product, since elution of enzymes is difficult.

INDUSTRIAL APPLICABILITY

The process for freeze-drying according to the present invention can beapplied for preserving, for transporting and for practical use byfreeze-drying bodies of organisms, organic substances, drugs, samples oforganisms, industrial raw materials and so on, which are subject todenaturation by the actions of oxygen, enzymes, heat and so on, in astate in which the original quality, properties and so on before thetreatment are preserved.

What is claimed is:
 1. A process for freeze-drying one or more materials, comprising the steps of: cooling the one or more materials by dry ice to freeze the one or more materials while breaking the one or more materials by subjecting the one or more materials to pressurization to cause the formation of cracks therein and subjecting the frozen one or more materials to vacuum drying.
 2. The process of claim 1, wherein more than one material is freeze-dried and the materials are cooled in a state wherein they are separated from each other.
 3. The process of claim 1, wherein more than one material is freeze-dried and the materials are cooled in a state wherein they are in contact with each other.
 4. The process of claim 1, wherein more than one material is freeze-dried and the materials are cooled in a state wherein portions of the materials are in contact with each other and portions of the materials are separated from each other.
 5. The process of claim 1, wherein the freezing is effected under a condition in which the one or more materials is pressurized by its own weight or by an external pressure.
 6. A freeze-dried product obtained by the process of claim
 1. 7. A food or drink comprising the freeze-dried product of claim
 6. 8. A composite product comprising the freeze-dried product of claim 6 compounded with another material.
 9. A process for freeze-drying materials comprising the steps of: stratifying the materials so that they are provided in multilayer form; interposing dry ice between layers of the multilayer materials; freezing the multilayer materials while breaking the multilayer materials by subjecting the multilayer materials to pressurization to cause the formation of cracks therein; and subjecting the frozen multilayer materials to vacuum drying.
 10. The process of claim 9, wherein the materials are of the same kind.
 11. The process of claim 9, wherein the materials are of different kinds.
 12. The process of claim 9, wherein the dry ice is intermittently interposed between the layers so that portions of the layers that are devoid of dry ice adhere to each other and vacant spaces are formed at portions of the layers where the dry ice is provided.
 13. The process of claim 9, wherein the freezing is effected under a condition in which the materials are pressurized by their own weight or by an external pressure.
 14. A freeze-dried product obtained by the process of claim
 9. 15. A food or drink comprising the freeze-dried product of claim
 14. 16. A composite product comprising the freeze-dried product of claim 14 compounded with another material.
 17. A hydrated product obtained by hydrating the freeze-dried product of claim
 6. 18. A hydrated product obtained by hydrating the freeze-dried product of claim
 14. 19. A composite product comprising the hydrated product of claim 17 compounded with another material.
 20. A composite product comprising the hydrated product of claim 18 compounded with another material. 